1. Field of the Invention
The present invention relates to an improved liner for the intake casing of a water jet propulsion pump. More particularly, the invention relates to a water jet propulsion pump which is an after market modification to an outboard motor used on small boats. The water jet propulsion pump, called a jet drive, replaces the propeller at the lower end of the outboard motor drive shaft.
The improved liner of the present invention for the intake casing of the jet drive is an accessory element which serves essentially two purposes: it increases the wear resistance of the jet drive intake casing to internal abrasion from ingested sand and gravel, and it lessens the likelihood of damage to the jet drive assembly by insulating the jet drive intake casing from the rest of the jet drive assembly with a shock absorbing material.
2. Description of the Prior Art
The inventor of the present invention is the originator and developer of water jet propulsion pump conversion units for outboard motors for boats. The history of the industry is chronicled by his patents which are included herein by reference.
Water jet propulsion pump conversions for outboard motors have a unique advantage over propeller drives which make them highly desirable in comparison to propeller drives for specific applications. Propeller drives are extremely vulnerable to damage due to the relatively fragile and intricate configuration of the propeller. Slight deformation of only one of the usually multiple blades of a propeller will greatly decrease if not destroy the efficiency of the propeller output. Even slight damage to a propeller blade due to a strike with an object can completely disable a motor by causing the motor to vibrate so violently as to dislocate the connection of the motor to the boat or to damage the motor or the boat by continued operation of the motor. For this reason, propeller-driven outboard motors cannot be utilized safely in shallow water where a propeller strike on the bottom might occur.
There are many shallow rivers and streams in the world where boats are needed for transportation and can be run if the use of a propeller-driven propulsion unit can be avoided. As a result of this need, the inventor hereof has developed water jet propulsion pumps to replace the propellers on standard outboard motors so that shallow water running can be accomplished by outboard motor powered boats, and these improvements in the art have been patented and are included hereby by reference.
The first of said patents was issued Mar. 26, 1963, under U.S. Pat. No. 3,082,732 for a Water Jet Motor for Boats. FIG. 1 of that patent shows an outboard motor 1 attached to a boat 2 and having a jet pump 4 attached to the lower end of the outboard motor. The jet drive has an intake section 7 which ingests water to the casing 8 which is then driven by the impeller 9, shown in FIG. 4, into the pump section. The impeller 9 is driven by the outboard motor drive shaft 10 and has vanes or blades 12 in the form of a screw which pressurize water through the recuperation section 13. The impeller accelerates the mass of the ingested water through the recuperation section 13 and out the nozzle 14 causing the reaction to drive the boat through the river or stream.
An improvement patent issued to the inventor of the present invention on Oct. 5, 1965, under U.S. Pat. No. 3,209,534 for Outboard Motor Exhaust System. That patent shows improvements in the means of operation of the earlier patented invention.
Another improvement patent was issued to the present inventor on Feb. 6, 1968, under U.S. Pat. No. 3,367,116 for An Intake Grill for Water Jet Pump. While this patent is directed to subject matter not related to the present invention, subject matter related to the present invention is disclosed therein but not claimed. FIGS. 3 and 5 thereof show the jet drive impeller 9 disposed in the intake casing 8. The casing is provided with a liner 16 which is supplied for the purpose of providing abrasion resistance to sand and gravel which might be ingested from a river bed or stream bottom and expelled through the pump. This liner is the closest known prior art to the present invention. However, it had several defects which were not easily overcome, and it did not prove successful until improvements were developed for the present invention almost 15 years later.
A further development in the art of jet drives was effected by the present inventor and is disclosed in the patent issued on Mar. 20, 1984, under U.S. Pat. No. 4,437,841 for An Outboard Jet Drive Steering Mechanism. The improvement permits jet boats to run in the very shallowest water possible that the boat can float in. There shown in FIGS. 1-3 is a current conceptualization of the jet drive apparatus illustrating the recuperation section as a nautilus type spiral volute. While the volute is not specifically numbered, it is designated by the numerals "28" in FIG. 1 and "20" in FIGS. 2 and 3. Disposed in the spiral volute of the jet drive assembly are the impeller blades 50, FIG. 1, which pressurize the water for expulsion out the jet drive nozzle 32. The volute is positioned immediately above the intake casing 52, FIG. 1, and 28, FIG. 3, in which the jet pump impeller 50, FIG. 1, is disposed.